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BUG: Copy categorical codes if empty (fixes #18051) #18279

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BUG: Copy categorical codes if empty (fixes #18051) #18279

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BUG: Copy categorical codes if empty (fixes #18051)
Nov 15, 2017
21734aa
Unit tests
Nov 20, 2017
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12 changes: 9 additions & 3 deletions pandas/tests/test_categorical.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1673,9 +1673,11 @@ def test_unique(self):
exp_cat = Categorical(["b", np.nan, "a"], categories=["b", "a"])
tm.assert_categorical_equal(res, exp_cat)

# GH 18051 unique()._codes should be writeable
cat_nan = Categorical([np.nan])
assert cat_nan.unique()._codes.flags.writeable
# GH 18051
cat = Categorical([np.nan])
res = cat.unique()
exp_cat = Categorical([np.nan], categories=[])
tm.assert_categorical_equal(res, exp_cat)
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@ghasemnaddaf ghasemnaddaf Nov 20, 2017 •
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@jreback , do you mean like this? (This is not failing on 0.21.0 though)

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@topper-123 topper-123 Nov 21, 2017 •
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There should be a test for

assert pd.Series(pd.Categorical([np.nan])).nunique() == 0

Note that nunique is a method on Series, not Categorical.

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@ghasemnaddaf ghasemnaddaf Nov 21, 2017 •
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@topper-123 I have added that test in https://github.com/pandas-dev/pandas/pull/18279/files#diff-ed4f442894a2f521dfac3193a3a8d8a0R2185 (L2185) below.

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@topper-123 topper-123 Nov 21, 2017 •
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That looks great IMO.

Also, you mention above that Categorical([np.nan]).unique() doesn't fail in 0.21.0, but pd.Series(pd.Categorical([np.nan])).unique() does fail. So if you could add a test for that as well in the test for series, then IMO the PR is good (but let @jreback make the final call on that).


def test_unique_ordered(self):
# keep categories order when ordered=True
Expand Down Expand Up @@ -2178,6 +2180,10 @@ def test_basic(self):
result = x.person_name.loc[0]
assert result == expected

# GH 18051
s = pd.Series(pd.Categorical([np.nan]))
assert s.nunique() == 0

def test_creation_astype(self):
l = ["a", "b", "c", "a"]
s = pd.Series(l)
Expand Down